1. Field of the Invention
The present invention concerns a short-arc type discharge lamp and a light-source device that uses a short-arc type discharge lamp.
2. Description of Related Art
In recent years, liquid-crystal projectors and DMD projectors have come into extensive use as presentation tools, and short-arc type discharge lamps, such as metal halide lamps or mercury lamps, have been used since high brightness is required of such light sources for projection. In addition, short-arc type xenon lamps have been used in projector light sources that project large pictures.
Short-arc type discharge lamps, for example, xenon lamps, have a pair of electrodes disposed facing each other within a quartz glass emission envelope in which xenon gas is sealed, and a sealing tube is connected to each of opposite sides of the emission envelope. Electrode core rods with electrodes formed at the tips are hermetically sealed within the sealing tube in step-seamed glass sealed lamps. The electrode core rods extend out from the step-seamed glass section and double as external lead rods, and the lead lines comprising twisted wires are connected to the tail edge of the external lead rods by soldering. In addition, the cylindrical bases with bottoms are bonded by adhesive to the sealing tube, and the external lead rods and the lead lines are covered by this base. The edge of the lead wire is connected to the terminal of the base.
The foil sealing method, in which the edge of the electrode core rod and the edge of the external lead rods are individually connected to metal foil and the metal foil is hermetically embedded in the sealing tube, may be used instead of the step-seamed glass sealing method.
Incidentally, projector light-source devices reach extremely high temperatures during lighting of xenon lamps that are disposed in the casing, and external lead rods made of tungsten or molybdenum also reach high temperatures. When external lead rods reach high temperatures, the step-seamed glass section also reaches high temperatures and distortion develops. Such distortion brings about cracking of step-seamed glass.
Furthermore, oxidation rapidly proceeds at high temperatures since the external lead rods within the base are exposed to the atmosphere. Force that spreads open quartz glass comprising the step-seamed glass sealing sections acts when such oxidation is transmitted to the section of the external lead rods within the sealing tube, and that also can generate cracking.
The external lead rods and metal foil within the foil seal section oxidize when a lamp reaches extremely high temperatures even in the case of a foil sealed lamp, and the quartz glass comprising the foil seal section cracks.
For this reason, a pair of ventilation apertures facing each other have been formed about the periphery of the base or cooling fins have been established on the outer surface of the base in the past. However, cooling air within the light-source device often flows along the axial direction of the lamp even if ventilation apertures are formed about the periphery of the base, so that little cooling air flows to the interior of the base from the ventilation aperture orthogonally to the axis of the lamp, and the external lead rods within the base cannot be adequately cooled. The cooling air entering the base and circulating along the external lead rods results in cooling only of a narrow region of the external lead rods. Furthermore, since cooling fins established on the outer surface of the base effect cooling by using the heating attributable to thermal conduction, the external lead rods within the base cannot be adequately cooled by these either.
Recently, limits have been imposed on the overall lamp length in light of the demand for miniaturization of projectors, and the gap between external lead rods and electrodes, which reach high temperatures during lighting, has become narrower. Accordingly, the temperature elevation of external lead rods has become increasingly pronounced, and the problem of shorter lamp life attributable to high temperature oxidation of external lead rods has been demonstrated.
Thus, the purpose of the present invention is to provide a short-arc type discharge lamp and a light-source device that uses a short-arc type discharge lamp in which high temperature oxidation of external lead rods is restricted to prolong lamp life.
To attain such objectives, the invention provides a short-arc type discharge lamp in which a pair of electrodes are disposed facing each other within an emission envelope made of quartz glass, external lead rods electrically connected to said electrodes extend from sealing tubes connected to each of opposite ends of the emission envelope, and are electrically connected to cylindrical bases with bottoms that are attached to at least one of the sealing tubes, a first aperture is formed for ventilation about the periphery of the bases and a second aperture for ventilation is formed at the tail edge of at least one of the bases to facilitate the circulation of cooling air within the bases and to thereby adequately cool the external lead rods within the bases.
Also in accordance with the invention, a heat dissipation section is formed at the external lead rods or the lead lines within the base. Additionally, according to the invention, a ventilation-concentration hood can be provided which conducts cooling air to the first aperture for ventilation, and that permits more efficient cooling of the external lead rods within the base.
The invention also concerns a light-source device in which the short-arc type discharge lamp and a concave reflection mirror surrounding this short-arc type discharge lamp are disposed in a casing, wherein a threaded section is formed about the periphery of the base, an attachment hole is formed in the lamp retaining plate, and the short-arc type discharge lamp is retained by inserting said base in the attachment hole of the lamp retaining plate and screwing it.